Process–property–performance relationships for titanium dioxide coatings engineered from nanostructured and conventional powders

Nanostructured (Nano), fused and crushed (F&C) and plasma-fused (PF) titania (TiO2) powder particles were thermally sprayed via flame spray (FS), air plasma spray (APS) and high velocity oxy-fuel (HVOF) on low carbon steel substrates. Flame spray processing, although widely employed industrially, generally has received very limited attention in academic papers. However, the results of this research have demonstrated that a FS Nano titania coating was the best performing among all coatings tested, exhibiting no measurable signs of mass/volume loss after dry-sliding wear testing (ball-on-disk) and the highest deposition efficiency (DE) level. This is regarded as an important result, considering the fact that among these three processing techniques FS is the least expensive, the most portable and exhibits the lowest energy consumption levels. In addition, scanning electron microscopy (SEM) analysis demonstrated that the sliding wear scars of the FS and HVOF-sprayed Nano coatings were smooth, without significant irreversible deformation or formation of ridges. These characteristics are not typical of ceramic materials. It is hypothesized that this plastic-like behaviour and resilience exhibited by FS and HVOF-sprayed Nano coatings explain their improved performance under dry-sliding wear.